Monthly Archives: September 2013

We interrupt our regularly scheduled blog to welcome Sam Jodka to Leveltek as a Regional Sales Director.  Sam is bringing his considerable experience in metal industry sales to Leveltek, including his years as a District Sales Manager with ThyssenKrupp in Columbus, Ohio. We couldn’t be happier to have him.

Welcome aboard, Sam!

Sam Jodka Leveltek Photo 2

Before we continue with the how and the what of lasers, we need to take a step back and briefly look at the history of this remarkable technology.  We found an old, but pleasantly brief and easy-to-follow description of where the technology came from, which we’ll share an updated version of here:

LASER is an acronym for “Light Amplification by Stimulated Emission of Radiation.”

Albert Einstein first explained the theory of stimulated emission in 1917, which became the basis of the laser. He postulated that, when the population inversion exists between upper and lower levels among atomic systems, it is possible to realize amplified stimulated emission, and the stimulated emission has the same frequency and phase as the incident radiation. However, it was in the late 1940s and 1950s that scientists and engineers did extensive work to realize a practical device based on the principle of stimulated emission.  Notable scientists who pioneered the work included Charles Townes, Joseph Weber, Alexander Prokhorov and Nikolai G. Basov.

Initially, the scientists and engineers were working towards the realization of a maser (“Microwave Amplification by the Stimulated Emission of Radiation”), a device that amplified microwaves for immediate application in microwave communication systems and does not use a visible light. Townes and the other engineers believed it to be possible to create an optical maser, a device for creating powerful beams of light using higher frequency energy to stimulate what was to become termed “the lasing medium.” Despite the pioneering work of Townes and Prokhorov, it was left to Theodore Maiman in 1960 to invent the first true laser, using ruby as a lasing medium that was stimulated using high energy flashes of intense light.

The development of lasers marked a turning point in the history of science and engineering. It produced a completely new type of system with the potential for applications in a wide variety of fields. During the 1960s, a lot of work had been carried out on the basic development of almost all the major laser types, including high-power gas dynamic and chemical lasers. Almost all the practical applications of these lasers in defense, as well as in industry, were also identified during this period. The motivation of using the high-power lasers in strategic scenarios was a great driving force for the rapid development of these high power lasers in the midst of the Cold War. In the early 1970s, a megawatt-class carbon dioxide gas dynamic laser was successfully developed and tested against typical military targets. The development of chemical lasers, free electron, and X-ray lasers took a slightly longer time because of the involvement of multidisciplinary approaches.

The major steps of advances or breakthroughs in laser research are given below:

1917: Einstein, A. – Concept and theory of stimulated light emission.

1948: Gabor, D. – Invention of holography.

1951: Townes, C.H., Prokhorov, A., Basov, N.G., Weber, J. – The invention of the maser at Columbia University, Lebedev Laboratories, Moscow, and the University of Maryland.

1956: Bloembergen, N. – Solid-state maser- [proposal for a new type of solid state maser] at Harvard University.

1958: Schawlow, A.L. and Townes, C.H. – Proposed the realization of masers for light and infrared at Columbia University.

1960: Maiman, T.H. – Realization of first working laser using rubies at Hughes Research Laboratories.

1961: Javan, A., Bennet, W.R. and Herriot, D.R. – First gas laser: helium-neon (He-Ne laser) at Bell Laboratories.

1961: Fox, A.G., Li, T. – Theory of optical resonators at Bell Laboratories.

1962: Hall, R. – First semiconductor laser (gallium-arsenide laser) at General Electric Labs.

1962: McClung, F.J and Hellwarth, R.W. – Giant pulse generation / Q-switching.

1962: Johnson, L.F., Boyd, G.D., Nassau, K and Sodden, R.R. – Continuous wave solid-state laser.

1964: Geusic, J.E., Markos, H.M., Van Uiteit, L.G. – Development of first working Nd:YAG laser at Bell Labs.

1964: Patel, C.K.N. –  Development of CO2 laser at Bell Labs.

1964: Bridges, W. – Development of argon ion laser a Hughes Labs.

1965: Pimentel, G. and Kasper, J.V.V. – First chemical laser at University of California, Berkley.

1965: Bloembergen, N. – Wave propagation in nonlinear media.

1966: Silfvast, W., Fowles, G. and Hopkins – First metal vapor laser – Zn/Cd – at the University of Utah.

1966: Walter, W.T., Solomon, N., Piltch, M and Gould, G. – Metal vapor laser.

1966: Sorokin, P. and Lankard, J. – Demonstration of first dye laser action at IBM Labs.

1966: AVCO Research Laboratory, USA. – First gas dynamic laser based on CO2

1970: Nikolai Basov’s Group – First excimer laser at Lebedev Labs, Moscow, based on xenon (Xe) only.

1974: Ewing, J.J. and Brau, C. –  First rare gas halide excimer at Avco Everet Labs.

1977: John M.J. Madey’s Group –  First free electron laser at Stanford University.

1977: McDermott, W.E., Pehelkin, N.R., Benard, D.J., and Bousek, R.R. – Chemical oxygen iodine laser (COIL).

1980: Geoffrey Pert’s Group – First report of x-ray lasing action, Hull University, UK.

1984: Dennis Matthew’s Group – First reported demonstration of a “laboratory” X-ray laser from Lawrence Livermore Labs.

1999: Herbelin, J.M., Henshaw, T.L., Rafferty, B.D., Anderson, B.T., Tate, R.F., Madden, T.J., Mankey II, G.C., and Hager, G.D. – All gas-phase chemical iodine laser (AGIL).

2001: Lawrence Livermore National Laboratory – Solid-state heat capacity laser (SSHCL).

Laser technology is incredibly important to what we do at Leveltek, and the mental image that probably elicits is a red beam cutting through metal.  Lasers are a LOT more Complicated than just a glorified Star Trek phaser!  Interested to know more?  Then let’s spend a few blog entries explaining just how lasers work, starting with the various types of lasers, straight from your high school physics class!

Commercial_laser_lines.svgDanh – Wikimedia Commons

There are many types of lasers available for research, medical, industrial, and commercial uses.  Lasers are often described by the kind of lasing medium they use – solid state, gas, excimer, dye, or semiconductor.

Solid state lasers have lasing material distributed in a solid matrix, e.g., the ruby or neodymium-YAG (yttrium aluminum garnet) lasers. The neodymium-YAG laser emits infrared light at 1.064 micrometers.

Gas lasers (helium and helium-neon, HeNe, are the most common gas lasers) have a primary output of a visible red light. CO2 lasers emit energy in the far-infrared, 10.6 micrometers, and are used for cutting hard materials.

Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases such as chlorine and fluorine mixed with inert gases such as argon, krypton, or xenon. When electrically stimulated, a pseudomolecule or dimer is produced and when lased, produces light in the ultraviolet range.

Dye lasers use complex organic dyes like rhodamine 6G in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.

Semiconductor lasers, sometimes called diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, e.g., the writing source in some laser printers or compact disk players.

Lasers are also characterized by the duration of laser emission – continuous wave or pulsed laser.  A Q-Switched laser is a pulsed laser which contains a shutter-like device that does not allow emission of laser light until opened.   Energy is built-up in a Q-Switched laser and released by opening the device to produce a single, intense laser pulse.

CONTINUOUS WAVE (CW) lasers operate with a stable average beam power. In most higher power systems, one is able to adjust the power. In low power gas lasers, such as HeNe, the power level is fixed by design and performance usually degrades with long term use.

SINGLE PULSED (normal mode) lasers generally have pulse durations of a few hundred microseconds to a few milliseconds. This mode of operation is sometimes referred to as long pulse or normal mode.

SINGLE PULSED Q-SWITCHED lasers are the result of an intracavity delay (Q-switch cell) which allows the laser media to store a maximum of potential energy. Then, under optimum gain conditions, emission occurs in single pulses; typically of 10(-8) second time domain. These pulses will have high peak powers often in the range from 10(6) to 10(9) Watts peak.

REPETITIVELY PULSED or scanning lasers generally involve the operation of pulsed laser performance operating at a fixed (or variable) pulse rates which may range from a few pulses per second to as high as 20,000 pulses per second. The direction of a CW laser can be scanned rapidly using optical scanning systems to produce the equivalent of a repetitively pulsed output at a given location.

MODE LOCKED lasers operate as a result of the resonant modes of the optical cavity which can effect the characteristics of the output beam. When the phases of different frequency modes are synchronized, i.e., “locked together,” the different modes will interfere with one another to generate a beat effect. The result is a laser output which is observed as regularly spaced pulsations. Lasers operating in this mode-locked fashion, usually produce a train of regularly spaced pulses, each having a duration of 10(-15) (femto) to 10(-12) (pico) sec. A mode-locked laser can deliver extremely high peak powers than the same laser operating in the Q-switched mode. These pulses will have enormous peak powers often in the range from 10(12) Watts peak.